Histopathologic study of the cochlear nuclei after 10 years of electrical stimulation of the human cochlea

This report provides histologic data on the cochlear nuclei of a patient who used a cochlear implant in the right ear for about 10 years and in the left ear for about 1 year. The most pronounced abnormality in the cochlear nuclei is sites of gliosis. However, since areas of necrosis with similar size, shape, and content of cells were observed outside the nuclei, the gliosis was not specific to the nuclei. There were no other unusual changes in the cochlear nuclei, such as excessive chromatolysis, excessive accumulation of lipofuscin, swollen neurons, or accumulation of glial cells. Comparison showed no statistically significant differences in sizes of cell bodies, size of nuclei, and total density of neurons in cochlear nuclei between the right and left sides. However, the density of normal-looking neurons (with visible nucleoli and without visible pathologic features) was noticeably less on the longer-stimulated side. Some differences between the longer- and shorter-stimulated sides may be due to differences before implantation or other factors, as well as to effects of stimulation.